Author Topic: Focus-Throw and Aperture Question on the Sigma 180mm APO Macro  (Read 4038 times)

Michael Erlewine

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Here is a lens question that well reveal my ignorance, but if you will answer it, then that ignorance will vanish.

I just picked up a used copy of the Sigma 180mm f/2.8 APO Macro EX DG OS HSM. This is a lens that has optical stabilization, which I have turned off.

My question is twofold. It does not have a separate aperture ring, so this gives me fits. If does have connection to the Nikon D810, but when I try to dial down the aperture (on the camera) to f/2.8, it won’t go that low. It stops at f/4. I am not clear why this is doing this, since I have few “G” type lenses.

The second question is that it claims to have a longer focus thrown, like -270 degrees. When I focus-stack with it, and move from the front to the back of, say, a flower, it takes very little turning to get from the front to the back, which does not give me enough layers of focus. I need it to take more turns.

When I put on a lens like the Leica Emarit-R 100mm Macro, with a focus throw of 720 degrees, there is a lot more turn to cover the same distance. So, my question is, if two lenses have a focus thrown (listed) of -270, can that vary so that one lens make take a longer time (more turning) to cover that distance, and another lens less time and less turning -- shorter distance? Obviously, I know the answer, but I am wondering why or how what works?
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Akira

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Re: Focus-Throw and Aperture Question on the Sigma 180mm APO Macro
« Reply #1 on: February 02, 2016, 21:52:09 »
As for the aperture value, you would need to focus at distance to get to f2.8.  If you focus closer, the actual speed of the lens will be slower, which occurs in any lenses.  Nikon system is, contrary to Canon, designed to indicate that.

I'm afraid I cannot say anything about the focus ring.  Please wait anyone else to chime in.
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PedroS

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Re: Focus-Throw and Aperture Question on the Sigma 180mm APO Macro
« Reply #2 on: February 02, 2016, 21:53:00 »
Macro G lenses, depending of the focus distance go faster or slower, so may be you are too close when it "blocks" the aperture on f4. Try at infinity, if it shows f2.8, everything is ok.
270 of focus throw is not much... and I think it would be critical on focus-stacking, as you experienced.

Don't have this particular lens, and never tried it, so can only rely on internet info...

Michael Erlewine

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Re: Focus-Throw and Aperture Question on the Sigma 180mm APO Macro
« Reply #3 on: February 02, 2016, 22:12:35 »
As a macro lens, I don't want to shoot at infinity and I need that f/2.8. Are you saying I can go to infinity and get f/2.8, and then focus closer, or will it than revert to f/4?
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Roland Vink

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Re: Focus-Throw and Aperture Question on the Sigma 180mm APO Macro
« Reply #4 on: February 02, 2016, 22:16:29 »
Question 1: My guess is the lens will get to f/2.8 when focused at far distances. At close range some light is lost due to extension (even though it is an IF lens) so the max aperture drops to f/4 at close range. It seems the Sigma is reporting the correct aperture to the camera, similar to Nikon macro lenses.

Some other macro lenses (especially manual lenses such as the CV 125/2.5 and ZF 100/2) don't report the loss in speed at close range, the aperture visible in the viewfinder and recorded in exif data is only true for the lens at far distances. At close range the aperture is overstated. For example the CV 125/2.5 wide open is only around f/4.5~F/5 at 1:1, not f/2.5. This can easily cause problems, you might think you are shooting at f/8, while you are actually shooting nearer to f/16 - well into diffraction territory.

Question 2: As for focus throw, are you sure you aren't confusing 270 deg with 720 deg? The Leica 100mm macro with 720 deg focus throw (2 full turns) to only 1:2 is obviously a LOT longer than the Sigma with 270 deg throw (3/4 turn) to 1:1. That's nearly three times the rotation to get to half the magnification.

Two lenses with the same focus throw and same maximum magnification, shooting a subject at the same magnification, will have the same turning to cover the same distance (for stacking etc). So, for example if you have a 100mm and 200mm macro lens, both with 300 deg focus throw, both get to 1:2 at close range - if you shoot the same subject at the same magnification (working distance is obviously different), then the focus throw to cover the subject will be similar (I think?)

Michael Erlewine

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Re: Focus-Throw and Aperture Question on the Sigma 180mm APO Macro
« Reply #5 on: February 02, 2016, 22:19:48 »
Thanks. That is what I thought.

Not confusing the focal lengths.
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PedroS

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Re: Focus-Throw and Aperture Question on the Sigma 180mm APO Macro
« Reply #6 on: February 02, 2016, 22:20:38 »
As a macro lens, I don't want to shoot at infinity and I need that f/2.8. Are you saying I can go to infinity and get f/2.8, and then focus closer, or will it than revert to f/4?

No, I couldn't find info about that, but I suspect it will never shot at f2.8 at closer distances, as some G lenses do.
In fact that's why a manual aperture ring is so helpful in macro work.

Previous post flagged a point... 270 is almost 3 times less throw vs 720...

Roland Vink

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Re: Focus-Throw and Aperture Question on the Sigma 180mm APO Macro
« Reply #7 on: February 02, 2016, 22:25:58 »
Not confusing the focal lengths.
No, but the wording in your original post made me wonder if you were confusing focus throw (720 / 270)

Akira

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Re: Focus-Throw and Aperture Question on the Sigma 180mm APO Macro
« Reply #8 on: February 02, 2016, 22:32:47 »
As a macro lens, I don't want to shoot at infinity and I need that f/2.8. Are you saying I can go to infinity and get f/2.8, and then focus closer, or will it than revert to f/4?

Michael, you have owned Micro Nikkors like 105/2.8 VR and 60/2.8 IF ED which behave the same way as the Sigma 180 Macro: focusing at closer distances, you won't get to f2.8.  The smallest aperture value of 60/2.8 IF ED when focused at 1:1 magnification will be as slow as f4.8.
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Roland Vink

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Re: Focus-Throw and Aperture Question on the Sigma 180mm APO Macro
« Reply #9 on: February 02, 2016, 22:47:10 »
As a macro lens, I don't want to shoot at infinity and I need that f/2.8.
The easiest way to get that is with the ZF 100/2 or 50/2 macro lenses. The aperture is f/2 at infinity, by the time you get to the close focus limit (1:2 magnification), the true aperture drops to f/2.8 (even though the reported aperture is still f/2).

Bjørn Rørslett

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Re: Focus-Throw and Aperture Question on the Sigma 180mm APO Macro
« Reply #10 on: February 02, 2016, 23:56:28 »
Nikon, and now apparently followed by Sigma, report the effective aperture at any focused distance. This is of course exactly the figure you need in order to calculate the correct exposure, whether light metering is in-camera or by external meters.  Brands that claim the aperture stays wide open at the infinity-focus value, will cause troubles and try to cheat you into believing their product defies optical laws.

Thus, f/2.8 for infinity focus becomes an effective f/4 at the near limit. Perfectly normal.

Michael Erlewine

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Re: Focus-Throw and Aperture Question on the Sigma 180mm APO Macro
« Reply #11 on: February 03, 2016, 01:49:08 »
Thanks everyone. I get it. Not sure I still have a "G" lens anymore. I don't use AF but for family photos, etc. A focus throw of 270 degrees in not enough for detailed stacked work IMO. Might as well put it on a rail.
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pluton

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Re: Focus-Throw and Aperture Question on the Sigma 180mm APO Macro
« Reply #12 on: February 03, 2016, 06:14:34 »
Wouldn't it be more honest for Nikon and Sigma to give the decreased light intensity at long extension a T stop value, rather than offering an f stop value that is geometrically innaccurate?
For example: My 55/3.5 Micro-Nikkor Ai, set with the aperture wide open, has not changed to a 55/7.1 when extended to 1:1.  It is delivering an effective T/7.1 at that extension.  Physically and geometrically, the aperture is still f/3.5.
Also, the altered f-value is not needed for TTL metering, since the meter is seeing through the lens, right?
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Michael Erlewine

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Re: Focus-Throw and Aperture Question on the Sigma 180mm APO Macro
« Reply #13 on: February 03, 2016, 15:12:52 »
I am still evaluating this lens, but a brief look at the Sigma 180 APO f/2.8 DG HSM OS shows me that while this lens works well in single-shot photos, this is not true if you want to stack, especially with a many-layer stack. This is because the focus-throw is only 270 degrees, which is more than many lens made for action-shooting have, but not enough for serious stacking IMO and work. By comparison, the Voigtlander CV-125 has a focus throw of about 630-degrees and the Leica 10mm Elmarit-R has a focus throw of 720-degrees. In that case, I would have to put the Sigma 180 on a focus rail which has finer interval-gradations. However, the lens does go to 1:1, which is good.

Although the lens is f/2.8, this will not be very usable except at infinity, although the lens is designed for macro work. This is due to what is called “effective aperture.” As with many lenses, the moment we focus close with the Sigma, the actual aperture jumps to f/4, not helpful for the best bokeh. I like f/2.8 or preferably better, like f/2 or f/1.2.

The lens is sharp enough when stopped down to f/4, but just a little soft wide-open. The lens has autofocus, something I seldom use in close-up photography. This lens has OS (Optical Stabilization), which means you can use it handheld, but at 3.6 lb. (1.63 kg), this is not something I would want to do too much of.

One very nice thing: it has is a detachable tripod foot/collar that is a pleasure to use, one that allows changing from horizontal to vertical format in seconds. It also helps distribute the weight on your camera mount. It does not have an aperture ring, which I don’t like, on principle. However, it does have 9 aperture blades, and good bokeh.

At 180-degrees, the lens allows me to stand back and still be close-in, which is a big help for live-critter action. It has auto-focus, which makes it helpful for fast-moving insects, etc.

Will I use this lens? Not for what I usually do. I will consider using it on a gimbal (or tripod) with its autofocus for flying insect and bird shots… perhaps. I do this now with the Micro-Nikkor 105mm VR lens, which weights 1.58 lb. (720 g), works well, goes to 1:1, has 9 (rounded) blades, a minimum focus range of 12-inches (30.48 cm), and f/2.8, but has no collar or image stabilization.

This lens IMO, which is sturdy and well-built, is for the wildlife photographer who wants to capture moving critters, although it really is too heavy for that work. Most of what it does, I don’t need. What it lacks is why I use other lenses, like a longer focus throw, a bit faster, not totally sharp wide open, better “micro-contrast,” for example.

Nikon D810, Sigma 180mm APO Macro, Zerene Stacker
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Bjørn Rørslett

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Re: Focus-Throw and Aperture Question on the Sigma 180mm APO Macro
« Reply #14 on: February 03, 2016, 16:08:06 »
Wouldn't it be more honest for Nikon and Sigma to give the decreased light intensity at long extension a T stop value, rather than offering an f stop value that is geometrically innaccurate?
For example: My 55/3.5 Micro-Nikkor Ai, set with the aperture wide open, has not changed to a 55/7.1 when extended to 1:1.  It is delivering an effective T/7.1 at that extension.  Physically and geometrically, the aperture is still f/3.5.
Also, the altered f-value is not needed for TTL metering, since the meter is seeing through the lens, right?

No, you are mistaken. The effective aperture takes the geometry into account. It is not a "T"-stop. That would be another (albeit related) figure.

While it can be argued that TTL metering takes care of the change in effective aperture, in a number of situations you actually need the effective f-number. Flash photography in the studio is but one of many examples.